Films, such as silicon films or semiconductor films, are known to be used for providing pixels for liquid crystal display devices. Such films have previously been processed (i.e., irradiated by an excimer laser and then crystallized) via excimer laser annealing (“ELA”) methods. Other more advantageous methods and systems for processing the semiconductor thin films for use in the liquid crystal displays and organic light emitting diode displays for fabricating large grained single crystal or polycrystalline silicon thin films using sequential lateral solidification (“SLS”) techniques have been described. For example, U.S. Pat. No. 6,322,625 issued to Im and U.S. patent application Ser. No. 09/390,537, the entire disclosures of which are incorporated herein by reference, and which are assigned to the common assignee of the present application, describe such SLS systems and processes. The patent documents describe certain techniques in which multiple areas on the semiconductor thin film are. e.g., sequentially irradiated.
The semiconductor films processed using the conventional system and processes often suffer from varying energy densities from one irradiated region of such thin film to the next. This primarily due to the fact that the laser beam fluence at least slightly varies from one shot to the next. For example, during the sequential irradiation of the neighboring regions of the thin film, the first region is irradiated by a first beam pulse (set of pulses) having a first energy fluence, the second region is irradiated by a second beam pulse (or set of pulses) having a second fluence which is at least slightly different that the fluence of the first beam pulse, and the third region is irradiated by a third beam pulse (or set of pulses) having a third fluence which is at least slightly different that the fluence of the second beam pulse, etc. Upon the irradiation of these areas, they can crystallize (e.g., due to at least partial melting). The resulting energy densities of the irradiated and crystallized first, second and third regions of the semiconductor thin film are all, at least to an extent, different from one another due to the varying fluences of the sequential beam pulses irradiating the neighboring regions.
The problem may arise after such fabrication of the semiconductor thin film, i.e., when thin-film transistor (“TFT”) devices are placed in such areas irradiated and crystallized regions having differing energy densities. In particular, the performance of such TFT devices situated in the crystallized regions of the film may vary from one device to another because of their energy density differences. For example, while the TFT devices placed in each of the crystallized regions (which may be uniform therein) generally have uniform characteristics and operate in a substantially the same manner within each such region, the TFT devices do not operate in the uniform manner from one crystallized region to another. This manifests itself in the fact that the same colors provided on the neighboring pixels of the display may appear different from one another.
Another problem of the unintended consequence of irradiating the neighboring regions of the semiconductor thin film with pulses each having a slightly differing fluences is that a transition from the one of these regions to the next consecutive region may be visible. This is due to the energy densities being different from one anther in the two neighboring regions, and because the transitions between the regions at the border regions thereof has a contrast from one to another because of such differing energy densities. Thus, it is possible that the transition between the first region to the next region is sharper than it may be intended.
Accordingly, it may be preferable to generate substrates which include the semiconductor films that reduce the effects of differing fluences of consecutive beam pulses irradiating neighboring regions of the semiconductor thin film, which later crystallize.